I haven't got a Katana but it's been on my wishlist for a while. All I can say is that I have the 2 knob Keeley comp and it's excellent. I've also got 5 Keeley modded pedals and all of them are also spot on. I would expect the boost to be of equal quality - should drive those valves into even more warmth I suspect
BNever used one, but I did a fair bit of research on them when I was designing my "HZD" pedal (I still haven't found time to buld the first production run of the HZDs... but I digress).
The Katana looks, on paper, extremely good. If I saw a used one here for $100 I'd buy it, but probably wouldn't pay more than that because there are other, cheaper options.